Alkylated diarylamines are known antioxidant compositions used as stabilizers in organic materials. Typically, these alkylated diarylamines are made by reacting an olefinic compound with diphenylamine in the presence of aluminum chloride catalyst. The resulting compounds are deeply colored, possibly due to strong activity of the catalyst or a reaction between the amine and the chloride. Such colored products have less appeal in the industry because certain antioxidant utilities require a high degree of purity or absence of colored contaminants, or simply because dark colored antioxidants are aesthetically less appealing.
Distillation may improve the color but often it is not enough since coloration reoccurs through oxidation of remaining contaminants. Therefore, it is desirable to find an adsorbent which can specifically remove the color contaminants generated from aluminum halide catalyst alkylation of diarylamines. Heretofore, decolorization of various amines required special adsorbents such as zinc, as disclosed in Reagents for Organic Synthesis, Vol. 1, p. 1281, Fiester & Fiester, 1967, bromine as disclosed in Derwent Abstract 117:25931b, page 649, Vol. 117, 1992, or ion-exchange resins, as disclosed in U.S. Pat. No. 5,097,041. Carbons, molecular sieves and silica gel which are common adsorbents for color contaminants as taught by Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed., Vol. 1, p. 532 (1978), do not work well at all. Clays are known decolorizers for vegetable, animal and petroleum oils, but are not known for amines. U.S. Pat. No. 4,824,601 discloses the use of activated earth catalysts to produce alkylated diphenylamine liquid antioxidant compositions lighter in color than those obtained using aluminum chloride catalyst. Additionally, to achieve bleaching and alkylation using clay catalyst, the reaction must occur at a relatively high temperature, 160.degree. C. or higher, which is not practical. Also, clay is a substantially less effective catalyst than aluminum chloride in that under equal conditions, substantially less diphenylamine is converted into product by clay as compared to aluminum chloride. This is demonstrated in Example 2 following herein. Therefore, it is more desirable to produce the alkylated diphenylamines using aluminum chloride catalyst. A new method of removing the color contaminants produced specifically from aluminum halide catalyzed alkylation of diarylamines has been discovered. The instant inventive method will enable the industry to utilize efficiently produced diarylamine antioxidant and subsequently decolorize it by a simple, efficient method of mixing and heating clay with the colorized antioxidants.